1. Field of the Invention
The present invention relates to a color picture tube apparatus with an in-line type electron gun.
2. Description of the Related Art
In a color picture tube with an in-line type electron gun, a misconvergence may occur due to a rotational shift of an electron gun during a sealing process of the electron gun and a rotational shift of a deflection yoke during a winding process and an assembly process.
Conventionally, in order to correct the above-mentioned misconvergence due to the rotational shifts, a color picture tube apparatus is known, in which a CPU (Convergence and Purity Unit) composed of each pair of dipole, quadrupole, and hexapole magnets is provided at a neck portion of a color picture tube, and a pair of annular additional quadrupole magnets are provided further on a screen side with respect to the CPU (e.g., see JP1(1989)-26146B).
For convenience of the following description, it is assumed that an axis in a horizontal direction (long side direction) passing through a tube axis and being vertical thereto is an X-axis, an axis in a vertical direction (short side direction) passing through the tube axis and being vertical thereto is a Y-axis, and the tube axis is a Z-axis. Furthermore, an in-line type electron gun refers to an electron gun in which three cathodes emitting electron beams of three colors B (blue), G (green), and R (red) are arranged in a line, and an in-line direction refers to a direction in which three cathodes are arranged. In the present specification, an in-line type electron gun will be described, in which an X-axis direction with three cathodes arranged on an X-axis is defined as an in-line direction.
In a conventional correction of a rotational shift according to JP1(1989)-26146B, as shown in FIG. 9A, a pair of annular additional quadrupole magnets 101a, 101b are rotated around a Z-axis while the rotation phases around the Z-axis are shifted from each other, whereby a quadrupole magnetic field is allowed to act on electron beams. However, the pair of additional quadrupole magnets 101a, 101b are rotated manually, so that a bisector X′ of a relative open angle θ between the pair of additional quadrupole magnets 101a, 101b may not be matched with an X-axis. In this case, electron beams B, R on both sides do not move in a Y-axis direction. Consequently, a new misconvergence may be caused as shown in FIG. 9B.